Method and apparatus for reproducing data and method and apparatus for recording and/or reproducing data

ABSTRACT

A magnetic recording and/or reproducing apparatus performing efficient decoding to lower a decoding error rate. A magnetic recording and/or reproducing apparatus  50  includes a modulation SISO decoder  63  for modulation decoding data modulation-encoded in a predetermined fashion by a modulation coder  52 . In the magnetic recording and/or reproducing apparatus  50 , the modulation SISO decoder  63  is a soft input soft output (SISO) type modulation decoder fed with a soft input signal and issuing a soft output signal. The modulation SISO decoder  63  is fed with a trellis soft output signal D 64  supplied from a trellis SISO decoder  62  to find a soft decision value for an error correction coding data D 52  fed to the modulation coder  52  of the recording system to generate a modulated soft decision signal D 65 . The modulation SISO decoder  63  routes the so-generated modulated soft decision signal D 65  to a downstream side error correction soft decoder  64.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and apparatus for reproducing datarecorded on a recording medium and a method and apparatus for recordingand/or reproducing data for a recording medium.

2. Description of Related Art

As a recording medium for recording digital data, there are known a widevariety of recording mediums of the magnetic, optical or photomagneticsystem, such as a hard disc, a so-called DVCR (digital video cassetterecorder) or a so-called CD (Compact Disc), DVD (digital versatile disc)and a so-called MO (magneto-optical disc).

For recording signals on these recording mediums, physical processingneeds to be performed on the recording mediums, such as by controllingthe direction of magnetization by a write head for a recording medium ofthe magnetic recording system, or by forming pits of lengthscorresponding to signals by a stamper for a recording medium of theoptical recording system. In this case, in order to permit amplitudecontrol of readout signals or clock reproduction on the reproducing sidereading out the signals recorded on the recording medium to operate asnormally, the signal recording side for recording signals on a recordingmedium routinely uses a system of modulation encoding the signal in apre-set manner to record the resulting modulation-coded signal.

A modulation-coder, performing this modulation coding, routinely is fedwith binary signals exempt from various limitations, and outputs binarysignals free of various limitations. These limitations on the signalsinclude DC free limitations which state that the numbers of “0”s and“1”s be equalized over a sufficient long length of the concatenations of“0”s and “1”s, and the (d, k) limitations which state that the minimumand maximum numbers of consecutive “0”s and “1”s in a code be d and k,respectively. FIG. 1 shows an input/output example in a modulation coderoutputting a code satisfying the (d, k)=(2, 7) limitations.Specifically, a modulation coder 150, outputting a code satisfying the(d, k)=(2, 7) limitation, is shown in FIG. 1, by way of concreteexplanation of the concept of the (d, k) limitations. That is, if aninput signal, free of the limitation, is input to the modulation coder150, outputting a code satisfying the (d, k)=(2, 7) limitation,modulation-encodes the input signal to generate and output an outputsignal in which the minimum and maximum numbers of consecutive “0”s are2 and 7, respectively.

The above example indicates that, in converting a bit string free of alimitation is converted into another bit string subjected to alimitation, the total number of the output bits is larger than that ofthe input bits. If the total number of input bits is K and the totalnumber of output bits is N, the ratio K/N is represented as a code rateR. This code rate R serves as an index indicating the efficiency of themodulation coding. If two or more modulation coders, generating outputsignals satisfying the same limitations, are compared to one another, amodulation coder having the high code rate R is able to encode moreinput bits for a given number of output bits than one having the lowcode rate R. Stated differently, a modulation coder having a high coderate R is able to record more information on a pre-set recording mediumthan one having a low code rate R.

The modulation coding may be classified into a block coding system inwhich input bits are divided into plural blocks of pre-set lengths andoutput bits generated are divided into plural blocks of pre-set lengthscorresponding to the blocks of the input bits, and a variable lengthcoding system, in which encoding units of input bits and output bitsassociated with the input bits are varied. For example, the so-called8/9 code or the 16/17 code, routinely used for modulation coding, belongto the block coding system, whilst the so-called (1, 7) RLL code or the(2, 7) RLL code belong to the variable length encoding system.

For example, in a block modulation encoding system, fed with two bits asinput bits, and generating three output bits satisfying the (d, k)=(0,2) limitations, a modulation coder has a conversion table as Table 1:

TABLE 1 Example of Conversion Table input bits output bits 00 011 01 10110 111 11 110

stored in e.g., a memory, not shown. The modulation coder referencesthis conversion table and finds, for each 2-bit input bits, anassociated 3-bit output bits, with the output bits being issued asoutput sequentially.

On the other hand, a modulation decoder for modulating-decoding themodulation-coded signals has a back-conversion table, as Table 2:

TABLE 2 Example of Back-Conversion Table input bit decoded bits 000 01001 00 010 10 011 00 100 11 101 01 110 11 111 10

corresponding to the conversion table of Table 1, stored in e.g., amemory, not shown. The modulation decoder references thisback-conversion table to find and sequentially output 2-bit decodedbits, associated with the 3-bit input bits.

FIG. 2 shows a typical modulation decoder 160 having at least a ROM(read-only memory) 161. The modulation decoder 160 is fed with an inputaddress signal D 161 to output the contents stored in an address of theROM 161 corresponding to this input address signal D161 as a demodulateddecoded signal D162. In actuality, if the input bits are back-convertedinto decoded bits in accordance with the back-conversion table shown inTable 2, the contents of the decoded bits are stored in addresses of aROM 161 of the modulation decoder 160, corresponding to the input bitsin Table 2. The decoded bits, stored in these addresses, are read out byway of performing the back-conversion.

FIG. 3 shows a typical modulation decoder 170 at least having acombination circuit 171. The modulation decoder 170 is fed with an inputsignal D171 and executes logical operations on the input signal D171 bythe combination circuit 171 to generate a modulated decoded signal D172.In actuality, if, in performing back conversion from the input bits tothe decoded bits in accordance with the back-conversion table of Table2, the three-bit input signal D171 is represented as (a₀, a₁, a₂) and atwo-bit modulated decoded signal D172 is represented as (b₀, b₁), themodulation decoder 170 generates the output bits (b₀, b₁) by thecombination circuit 171 corresponding to the following logical equations(1):

b ₀=(a ₁&a ₂)|(a ₀&!a ₁&!a ₂)|(!a ₀&a ₁&!a ₂)

b ₁=(a ₀&!a ₁)|(!a ₀&!a ₁&!a ₂)|(a ₀&a ₁&!a ₂)  (1)

where |, & and ! indicate the logical sum, logical product and logicalnegation, respectively.

If the modulation coder and the modulation decoder are applied to amagnetic recording and/or reproducing apparatus for recording and/orreproducing data on or from a recording medium in accordance with themagnetic recording system, the recording and/or reproducing apparatus isconfigured as shown in FIG. 4.

That is, the magnetic recording and/or reproducing apparatus 200, shownin FIG. 4, includes, as a recording system for recording data on arecording medium 250, an error correction encoder 201 for errorcorrection encoding input data, a modulation encoder 202 for modulationencoding the input data, a precoder 203 for filtering input data forcompensating its channel characteristics, a write current driver 204 forconverting respective bits of the input data into write current values,and a write head 205 for recording data on the recording medium 250. Themagnetic recording and/or reproducing apparatus 200 also includes, as aplayback system for reproducing data recorded on the recording medium250, a readout head 206 for reading out data recording on the recordingmedium 250, an equalizer 207 for equalizing the input data, a gainadjustment circuit 208 for adjusting the gain of the input data, ananalog/digital converter (A/D converter) 209 for converting analog datainto digital data, a timing generating circuit 210 for generatingclocks, a gain adjustment control circuit 211 for controlling the gainadjustment circuit 208, a viterbi decoder 212 for viterbi-decoding theinput data, a modulation decoder 213 for modulation decoding the inputdata and an error correction decoder 214 for error correction decodingthe input data.

In recording data on the recording medium 250, the magnetic recordingand/or reproducing apparatus 200 performs the following operations:

When fed with the input data D201, the magnetic recording and/orreproducing apparatus 200 applies error correction coding to the inputdata D201, by the error correction encoder 201, to generate errorcorrection encoded data D202.

The magnetic recording and/or reproducing apparatus 200 modulationencodes the error correction encoded data D202 from the error correctionencoder 201, by the modulation encoder 202, to generatemodulation-encoded data D203, which is a string of bits subjected tolimitations.

The magnetic recording and/or reproducing apparatus 200 performsfiltering on the modulation-encoded data D203, supplied from themodulation encoder 202, by the precoder 203, in such a manner as tocompensate for the channel characteristics as from the writing of dataon the recording medium 250 up to outputting thereof at an equalizer 207in the reproducing system, to generate a precode signal D204. Forexample, if the channel has 1−D characteristics, the precoder 203performs the filtering F indicated by the following equation (2):

F=1/(1⊕D)  (2)

where ⊕ denotes exclusive-OR.

The magnetic recording and/or reproducing apparatus 200 then convertsrespective bits of the precode signal D204, as binary signal suppliedfrom the precoder 203, by a write current driver 204, into write currentvalues Is, such as by 0→−I_(S), 1→+I_(S), to generate a write currentsignal D205.

By the write head 205, the magnetic recording and/or reproducingapparatus 200 applies a write magnetization signal D206, correspondingto the write current signal D205 supplied from the write current driver204, to the recording medium 250.

By the above processing, the magnetic recording and/or reproducingapparatus 200 is able to record data on the recording medium 250.

In reproducing the data recorded on the recording medium 250, themagnetic recording and/or reproducing apparatus 200 performs thefollowing processing:

First, the magnetic recording and/or reproducing apparatus 200 reads outthe readout magnetization signal D207 from the recording medium 250 bythe readout head 206 to generate a readout current signal D208conforming to this readout magnetization signal D207.

The magnetic recording and/or reproducing apparatus 200 then equalizesthe readout current signal D208, supplied from the readout head 206, bythe equalizer 207, so that the channel response since data writing onthe recording medium 250 in the recording system until outputtingthereof at the equalizer 207 will be of pre-set characteristics, such as1−D, to generate an equalized signal D209.

The magnetic recording and/or reproducing apparatus 200 then adjusts thegain of the equalized signal D209, supplied from the equalizer 207, bythe gain adjustment circuit 208, based on a gain adjustment controlsignal D213 from the gain adjustment control circuit 211, to generate again adjustment signal D210. Meanwhile, the gain adjustment controlsignal D213 is generated by the gain adjustment control circuit 211,based on the digital channel signal D211, as later explained.Specifically, the gain adjustment control signal D213 is a controlsignal for maintaining the amplitude of the equalization signal D209 atan expected value.

By the A/D converter 209, the magnetic recording and/or reproducingapparatus 200 digitizes the gain adjustment signal D210, supplied fromthe gain adjustment circuit 208, to generate the digital channel signalD211. Meanwhile, the A/D converter 209 performs sampling based on theclock signal D212 generated and supplied by the timing generatingcircuit 210. The timing generating circuit 210, fed with the digitalchannel signal D211, generates clocks to produce clock signals D212which are output to the A/D converter 209.

The magnetic recording and/or reproducing apparatus 200 feeds thedigital channel signal D211, supplied from the A/D converter 209, to theviterbi decoder 212, which then performs viterbi decoding on the channelresponse from the upstream side of the precoder 203 in the recordingsystem up to the outputting at the equalizer 207 in the reproducingsystem, for example, the channel response R_(ch) represented by thefollowing equation (3):

R _(ch)=(1−D)/(1⊕D)  (3)

where ⊕ denotes Exclusive-OR.

The magnetic recording and/or reproducing apparatus 200 then appliesmodulation decoding on the viterbi decoded signal D214, supplied fromthe modulation decoder 213, to realize data correspondence reversed fromthat in the modulation encoder 202 in the recording system to generate amodulated decoded signal D215 which is an original input data string notsubjected to limitations.

The magnetic recording and/or reproducing apparatus 200 decodes theerror correction codes of the modulated decoded signal D215, suppliedfrom the modulation decoder 213, by the error correction decoder 214, togenerate output data D216.

By the above processing, the magnetic recording and/or reproducingapparatus 200 is able to reproduce the data recorded on the recordingmedium 250.

Meanwhile, in the above-described conventional magnetic recording and/orreproducing apparatus 200, the modulation decoder 213 has no more thanthe function of realizing the correspondence between binary signalsreversed from that obtained on modulation encoding by the modulationencoder 202, while the signals in both the input and the output of themodulation decoder 213 needs to be binary signals, with the result thatthe signals on the downstream side of the viterbi decoder 212 are allbinary signals.

In other words, it is necessary in the magnetic recording and/orreproducing apparatus 200 to generate binary signals on the upstreamside of the modulation decoder 213 and to process the binary signalseven on the downstream side of the modulation decoder 213.

Thus, in the magnetic recording and/or reproducing apparatus 200, inwhich bi-level binary signals need to be used, the information volume inthe signal is diminished intentionally with the result that efficientdecoding cannot be realized to deteriorate the decoding error rate.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a methodand apparatus for reproducing data recorded on a recording medium and amethod and apparatus for recording and/or reproducing data for arecording medium, whereby decoding may be performed efficiently to lowerthe decoding error rate.

In one aspect, the present invention provides a data reproducingapparatus for reproducing data recorded on a recording medium includingmodulation decoding means for modulation decoding datamodulation-encoded in a predetermined fashion by modulation encodingmeans provided on a recording equipment adapted for recording data onthe recording medium, in which the modulation decoding means is fed witha soft input signal and outputs a soft output signal.

This data reproducing apparatus modulation-decodes the datamodulation-encoded by soft input soft output type modulation decodingmeans.

In another aspect, the present invention provides a data reproducingmethod for reproducing data recorded on a recording medium including amodulation decoding step of modulation decoding data modulation-encodedin a predetermined fashion by a modulation encoding step for recordingdata on the recording medium, in which the modulation decoding step isfed with a soft input signal and outputs a soft output signal.

This data reproducing method modulation-decodes the datamodulation-encoded by a soft input soft output type modulation decodingstep.

In still another aspect, the present invention provides a data recordingand reproducing apparatus for recording and reproducing data for arecording medium, including modulation encoding means, as a recordingsystem for recording data on the recording medium, for performingpredetermined modulation encoding on the data in recording the data onthe recording medium, and modulation decoding means, as a reproducingsystem for reproducing the data recorded on the recording medium, formodulation-decoding data modulation-encoded by the predeterminedmodulation encoding by the modulation encoding means, in which themodulation decoding means is fed with a soft input signal and outputs asoft output signal.

This data reproducing apparatus modulation-decodes datamodulation-encoded by modulation encoding means by soft input softoutput type modulation decoding means.

In yet another aspect, the present invention provides a data recordingand reproducing method for recording and reproducing data for arecording medium, including a modulation encoding step of performingpredetermined modulation encoding on data recorded on the recordingmedium, as a recording system for recording data on the recordingmedium, and a modulation decoding step of modulation encoding datamodulation-encoded by the predetermined modulation encoding step, as areproducing system for reproducing data recorded on the recordingmedium, in which the modulation decoding step is fed with a soft inputsignal and outputs a soft output signal.

In this data reproducing method, a soft input signal is fed and a softoutput signal is issued in modulation-decoding data modulation-encodedby a modulation encoding step.

The data reproducing apparatus for reproducing data recorded on arecording medium according to the present invention includes modulationdecoding means for modulation decoding data modulation-encoded in apredetermined fashion by modulation encoding means provided on arecording equipment, configured for recording data on the recordingmedium. The modulation decoding means is fed with a soft input signaland outputs a soft output signal.

So, with the data reproducing apparatus according to the presentinvention, in which data modulation encoded in a predetermined fashionis modulation-decoded by soft input soft output modulation decodingmeans, efficient decoding exploiting the soft information may berealized, thereby lowering the decoding error rate.

The data reproducing method for reproducing data recorded on a recordingmedium according to the present invention includes a modulation decodingstep of modulation decoding data modulation-encoded in a predeterminedfashion in a modulation encoding step of recording data on the recordingmedium. The modulation decoding step is fed with a soft input signal andoutputs a soft output signal.

So, with the data reproducing method according to the present invention,a soft input signal is input and a soft output signal is output inmodulation-decoding data modulation-encoded in the modulation decodingstep to effect efficient decoding exploiting the soft information tolower the decoding error rate.

The data recording and reproducing apparatus for recording andreproducing data for a recording medium according to the presentinvention includes modulation encoding means, as a recording system forrecording data on the recording medium, for performing predeterminedmodulation encoding on the data in recording the data on the recordingmedium, and modulation decoding means, as a reproducing system forreproducing the data recorded on the recording medium, formodulation-decoding data modulation-encoded by the predeterminedmodulation encoding by the modulation encoding means. The modulationdecoding means is fed with a soft input signal and outputs a soft outputsignal.

So, in the data recording and reproducing apparatus according to thepresent invention, in which, in modulation decoding data modulation,encoded in a predetermined fashion by the modulation encoding means, bysoft input soft output modulation decoding means, efficient decodingexploiting the soft information can be achieved thereby lowering thedecoding error rate.

The data recording and reproducing method for recording and reproducingdata for a recording medium according to the present invention includesa modulation encoding step for performing predetermined modulationencoding on the data in recording the data on the recording medium, as arecording system for recording data on the recording medium, and amodulation decoding step for modulation decoding the datamodulation-encoded by the predetermined modulation encoding step, as areproducing system for reproducing data recorded on the recordingmedium. The modulation decoding step is fed with a soft input signal andoutputs a soft output signal.

So, in the data recording and reproducing method, according to thepresent invention, a soft input signal is input and a soft output signalis output in modulation decoding data modulation-encoded in themodulation decoding step to enable efficient decoding using the softinformation thus lowering the decoding error rate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an input/output example of a conventional modulationencoder.

FIG. 2 is a block diagram showing the structure of a conventionalmodulation decoder.

FIG. 3 is a block diagram showing the structure of another conventionalmodulation decoder.

FIG. 4 is a block diagram showing the structure of a conventionalmagnetic recording and/or reproducing apparatus.

FIG. 5 illustrates an input/output example in a modulation decoderapplied to a reproducing system of a magnetic recording and/orreproducing apparatus shown as a first embodiment of the presentinvention.

FIG. 6 is a block diagram showing the structure of a mediation decoderapplied to a reproducing system of the magnetic recording and/orreproducing apparatus shown in FIG. 5.

FIG. 7 is a block diagram for illustrating the structure of the magneticrecording and/or reproducing apparatus shown in FIG. 5.

FIG. 8 illustrates a status transition for generating codes satisfying(d, k)=(0, 2) limitations.

FIG. 9 illustrates a trellis following three times of status transitionin accordance with the status transition diagram shown in FIG. 8.

FIG. 10 illustrates a trellis constructed on branch selection from thetrellis shown in FIG. 9.

FIG. 11 is a block diagram for illustrating the structure of amodulation trellis encoder applied to a recording system of the magneticrecording and/or reproducing apparatus shown as a second embodiment ofthe present invention.

FIG. 12 is a block diagram for illustrating the structure of amodulation trellis encoder applied to a recording system of a magneticrecording and/or reproducing apparatus according to a second embodimentof the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, preferred embodiments of the presentinvention will be explained in detail.

The present embodiment is directed to a magnetic recording and/orreproducing apparatus made up of a recording system for recording dataon a recording medium of the magnetic recording system, such as a harddisc or a so-called DVCR (digital video cassette recorder), and areproducing system for reproducing data recorded on these recordingmediums.

This magnetic recording and/or reproducing apparatus uses a modulationdecoder of the soft input soft output type (SISO type), as a modulationdecoder for modulating and decoding modulation encoded signals, which isfed with data as soft input and which outputs data as soft output.

First, a magnetic recording and/or reproducing apparatus of a firstembodiment is explained. Here, the SISO type modulation decoder, asmodulation decoding means applied to the reproducing system of thismagnetic recording and/or reproducing apparatus, is explained byreferring to FIGS. 5 and 6.

A modulation decoder 10, shown in FIG. 5, decodes data encoded by blockmodulation, with the code rate R=k/n, where k is the number of inputbits and n is the number of bits for modulation coding.

When fed with a reception signal R as the soft input, the modulationdecoder 10 calculates the probability P (R_(i)=0|R) that the respectivebits of this reception signal R be “0” and the probability P (R_(i)=1|R)that the respective bits of this reception signal R be “1”. Ultimately,the modulation decoder 10 calculates a posterior probability informationP (Mi=0|R) and P (Mi=1|R), as a soft decision value for a modulationcode block M represented by M=(M₀, M₁, . . . , M_(n-1)), and/or aposterior probability information P (C_(i)=0|R) and P (C_(i)=1|R), as asoft decision value for a modulation code input block C represented byC=(C₀, C₁, . . . , C_(k-1)), to output the so-calculated information.

Instead of individually outputting the aforementioned posteriorprobability information, the modulation decoder is also able to outputthe logarithmic value of the ratio of the posterior probabilityinformation, that is log(P(M_(i)=1|R)/P(M_(i)=0|R)) orlog(P(C_(i)=1|R)/P(C_(i)=0|R)). These log values are routinely termedlog likelihood ratio and here denote the likelihood of the modulatingcode block M and the modulating code input block C on the occasion ofinputting the reception signal R.

The modulation decoder may also be fed with the priori probabilityinformation P (C_(i)=0) and P (C_(i)=1) for a modulation code inputblock C, instead of being fed with the aforementioned reception signalR.

Specifically, the modulation decoder may, for example, be configured asshown in FIG. 6. In the following explanation, it is assumed that, forgenerating a three-bit output for a two-bit input, data to be decodedhas been encoded in accordance with the conversion table shown in thefollowing Table 3:

TABLE 3 Example of Conversion Table input bits output bits 00 011 01 10110 111 11 110

The modulation decoder 20, shown in FIG. 6, includes six likelihoodcalculating circuits 21 ₁, 21 ₂, 21 ₃, 21 ₄, 21 ₅ and 21 ₆, as means forcalculating the likelihood of each reception bit, four adders 22 ₁, 22₂, 22 ₃ and 22 ₄ for summing the data, four log-sum circuits 23 ₁, 23 ₂,23 ₃ and 23 ₄ for performing the operations of log (e^(A)+e^(B)) on thetwo data A and B, four adders 24 ₁, 24 ₂, 24 ₃ and 24 ₄ for summing twodata and two comparators 25 ₁, 25 ₂ for taking the ratio of the twodata. It is noted that the number six of the likelihood calculatingcircuits is derived from three bits multiplied by 2 equals to six bits.

The likelihood calculating circuits 21 ₁, 21 ₂, 21 ₃, 21 ₄, 21 ₅ and 21₆ are respectively fed with respective reception bits in a receptionsignal D21 (R) to calculate the likelihood of the respective receptionbits.

That is, the likelihood calculating circuits 211 is fed with the 0th bitof the three-bit reception signal D21 to calculate the log probabilityvalue D22 ₁(logP(R₀=0|R)) corresponding to the log value of theprobability that this bit is “0”. The likelihood calculating circuits 21₁ sends the generated log probability value D22 ₁ to the adder 22 ₁.

The likelihood calculating circuits 21 ₂ is fed the 0th bit of thethree-bit reception signal D21 to calculate the log probability valueD22 ₂(logP(R₀=1|R)) corresponding to the log value of the probabilitythat this bit is “1”. The likelihood calculating circuits 21 ₂ sends thegenerated log probability value D22 ₂ to the adders 22 ₂, 22 ₃ and 22 ₄.

Then, the likelihood calculating circuits 21 ₃ is fed with the first bitof the three-bit reception signal D21 to calculate the log probabilityvalue D22 ₃ (logP(R₁=0|R)) corresponding to the log value of theprobability that this bit is “0”. The likelihood calculating circuits 21₃ sends the generated log probability value D22 ₃ to the adder 22 ₂.

The likelihood calculating circuits 21 ₄ is fed the first bit of thethree-bit reception signal D21 to calculate the log probability valueD22 ₄ (logP(R₁=1|R)) corresponding to the log value of the probabilitythat this bit is “1”. The likelihood calculating circuits 21 ₄ sends thegenerated log probability value D22 ₄ to the adder 22 ₁, 22 ₃ and 22 ₄.

Then, the likelihood calculating circuits 21 ₅ is fed with the secondbit of the three-bit reception signal D21 to calculate the logprobability value D22 ₅(logP(R₂=0|R)) corresponding to the log value ofthe probability that this bit is “0”. The likelihood calculatingcircuits 21 ₅ sends the generated log probability value D22 ₅ to theadder 22 ₄.

The likelihood calculating circuits 21 ₆ is fed the second bit of thethree-bit reception signal D21 to calculate the log probability valueD22 ₆(logP(R₂=1|R)) corresponding to the log value of the probabilitythat this bit is “1”. The likelihood calculating circuits 21 ₆ sends thegenerated log probability value D22 ₆ to the adders 22 ₁, 22 ₂ and 22 ₃.

The adder D22 ₁ sums the log probability value D22 ₁, supplied from thelikelihood calculating circuits 21 ₁, the log probability value D22 ₄,supplied from the likelihood calculating circuits 21 ₄ and the logprobability value D22 ₆, supplied from the likelihood calculatingcircuits 21 ₆ to generate the likelihood value D23 ₁. That is, thislikelihood value D23 ₁ is not other than the probability represented bylog P(R|M₀M₁M₂=011). The adder D22 ₁ sends the generated likelihoodvalue D23 ₁ to the log-sum circuits 23 ₁, 23 ₃.

The adder D22 ₂ sums the log probability value D22 ₂, supplied from thelikelihood calculating circuits 21 ₂, the log probability value D22 ₃,supplied from the likelihood calculating circuits 21 ₃ and the logprobability value D22 ₆, supplied from the likelihood calculatingcircuits 21 ₆ to generate the likelihood value D23 ₂. That is, thislikelihood value D23 ₂ is not other than the probability represented bylog P(R|M₀M₁M₂=101). The adder D22 ₂ sends the generated likelihoodvalue D23 ₂ to the log-sum circuits 23 ₁, 23 ₄.

The adder D22 ₃ sums the log probability value D22 ₂, supplied from thelikelihood calculating circuits 21 ₂, the log probability value D22 ₄,supplied from the likelihood calculating circuits 21 ₄ and the logprobability value D22 ₆, supplied from the likelihood calculatingcircuits 21 ₆ to generate the likelihood value D23 ₃. That is, thislikelihood value D23 ₃ is not other than the probability represented bylog P(R|M₀M₁M₂=111). The adder D22 ₃ sends the generated likelihoodvalue D23 ₃ to the log-sum circuits 23 ₂, 23 ₃.

The adder D22 ₄ sums the log probability value D22 ₂, supplied from thelikelihood calculating circuits 21 ₂, the log probability value D22 ₄,supplied from the likelihood calculating circuits 21 ₄ and the logprobability value D22 ₅, supplied from the likelihood calculatingcircuits 21 ₅ to generate the likelihood value D23 ₄. That is, thislikelihood value D23 ₄ is not other than the probability represented bylog P(R|M₀M₁M₂=110). The adder D22 ₄ sends the generated likelihoodvalue D23 ₄ to the log-sum circuits 23 ₂, 23 ₄.

The log-sum circuit 23 ₁ performs an operation shown by the equation(4):

log(e ^(logP(R|M) ^(₀) ^(M) ^(₁) ^(M) ^(₂) ⁼⁰¹¹⁾ +e ^(logP(R|M) ^(₀)^(M) ^(₁) ^(M) ^(₂) ⁼¹⁰¹⁾)=log(P(R|M ₀ M ₁ M ₂=011)+P(R|M ₀ M ₁ M₂=101))  (4)

on the likelihood value D23 ₁ supplied from the adder 22 ₁ and on thelikelihood value D23 ₂ supplied from the adder 22 ₂ to generate alikelihood value D24 ₁. The log-sum circuit 23 ₁ sends the so-generatedlikelihood value D24 ₁ to the adder 24 ₁.

The log-sum circuit 23 ₂ performs an operation shown by the equation(5):

log(e ^(logP(R|M) ^(₀) ^(M) ^(₁) ^(M) ^(₂) ⁼¹¹¹⁾ +e ^(logP(R|M) ^(₀)^(M) ^(₁) ^(M) ^(₂) ⁼¹¹⁰⁾)=log(P(R|M ₀ M ₁ M ₂=111)+P(R|M ₀ M ₁ M₂=110))  (5)

on the likelihood value D23 ₃ supplied from the adder 22 ₃ and on thelikelihood value D23 ₄ supplied from the adder 22 ₄ to generate alikelihood value D24 ₂. The log-sum circuit 23 ₂ sends the so-generatedlikelihood value D24 ₂ to the adder 24 ₂.

The log-sum circuit 23 ₃ performs an operation shown by the equation(6):

log(e ^(logP(R|M) ^(₀) ^(M) ^(₁) ^(M) ^(₂) ⁼⁰¹¹⁾ +e ^(logP(R|M) ^(₀)^(M) ^(₁) ^(M) ^(₂) ⁼¹¹¹⁾)=log(P(R|M ₀ M ₁ M ₂=011)+P(R|M ₀ M ₁ M₂=111))  (6)

on the likelihood value D23 ₁ supplied from the adder 22 ₁ and on thelikelihood value D23 ₃ supplied from the adder 22 ₃ to generate alikelihood value D24 ₃. The log-sum circuit 23 ₃ sends the so-generatedlikelihood value D24 ₃ to the adder 24 ₃.

The log-sum circuit 23 ₄ performs an operation shown by the equation(7):

log(e ^(logP(R|M) ^(₀) ^(M) ^(₁) ^(M) ^(₂) ⁼¹⁰¹⁾ +e ^(logP(R|M) ^(₀)^(M) ^(₁) ^(M) ^(₂) ⁼¹¹⁰⁾)=log(P(R|M ₀ M ₁ M ₂=101)+P(R|M ₀ M ₁ M₂=110))  (7)

on the likelihood value D23 ₂ supplied from the adder 22 ₂ and on thelikelihood value D23 ₄ supplied from the adder 22 ₄ to generate alikelihood value D24 ₄. The log-sum circuit 23 ₄ sends the so-generatedlikelihood value D24 ₄ to the adder 24 ₄.

The adder 24 ₁ sums the likelihood value D23 ₁ supplied from the log-sumcircuit 23 ₁ and the log priori probability D25 ₁(logP(C₀=0)) for aninput bit, fed from outside, to generate the log probability value D26₁. This log probability value D26 ₁ denotes the probability shown by thefollowing equation (8):

logP(C ₀=0|R)=log{P(R|M ₀ M ₁ M ₂=011)+(R|M ₀ M ₁ M ₂=101)}+logP(C₀=0)  (8).

The adder 24 ₁ sends the generated log probability value D26 ₁ to acomparator 25 ₁.

The adder 24 ₂ suns the likelihood value D24 ₂ supplied from the log-sumcircuit 23 ₂ and the log priori probability D25 ₂ (logP(C₀=1)) for aninput bit, input from outside, to generate the log probability value D26₂. This log probability value D26 ₂ denotes the probability shown by thefollowing equation (9):

logP(C ₀=0|R)=log{P(R|M ₀ M ₁ M ₂=111)+(R|M ₀ M ₁ M ₂=110)}+logP(C₀=0)  (9).

The adder 24 ₂ sends the generated log probability value D26 ₂ to acomparator 25 ₁.

The adder 24 ₃ sums the likelihood value D24 ₃ supplied from the log-sumcircuit 23 ₃ and the log priori probability D25 ₃ (logP(C₁=0)) for aninput bit, input from outside, to generate the log probability value D26₃. This log probability value D26 ₃ denotes the probability shown by thefollowing equation (10):

logP(C ₀=0|R)=log{P(R|M ₀ M ₁ M ₂=011)+(R|M ₀ M ₁ M ₂=111)}+logP(C₀=0)  (10)

The adder 24 ₃ sends the generated log probability value D26 ₃ to acomparator 25 ₂.

The adder 24 ₄ sums the likelihood value D24 ₄ supplied from the log-sumcircuit 23 ₄ and the log priori probability D25 ₄ (logP(C₁=1)) for aninput bit, input from outside, to generate the log probability value D26₄. This log probability value D26 ₄ denotes the probability shown by thefollowing equation (11):

logP(C ₀=0|R)=log{P(R|M ₀ M ₁ M ₂=101)+(R|M ₀ M ₁ M ₂=110)}+logP(C₀=0)  (11)

The adder 24 ₄ sends the generated log probability value D26 ₄ to acomparator 25 ₂.

The comparator 25 ₁ takes the ratio of the log probability value D26 ₁supplied from the adder 24 ₁ and the log probability value D26 ₂supplied from the adder 24 ₂ to generate the decoded log posteriorprobability ratio D27 ₁ (log(P(C₀=1|R)/P(C₀=0|R))) which is output.

The comparator 25 ₂ takes the ratio of the log probability value D26 ₃supplied from the adder 24 ₃ and the log probability value D26 ₄supplied from the adder 24 ₄ to generate the decoded log posteriorprobability ratio D27 ₂ (log(P(C₁=1|R)/P(C₁=0|R))) which is output.

The modulation decoder 20, having the components as described above, hasthe likelihood calculating circuits 21 ₁, 21 ₂, 21 ₃, 21 ₄, 21 ₅ and 21₆ for calculating the likelihood of respective reception bits in thereception signals D21(R) taking analog values under the effect of thenoise generated in the course of transmission, as soft input, that isthe respective output codewords on the modulation coder side. By theselikelihood calculating circuits 21 ₁, 21 ₂, 21 ₃, 21 ₄, 21 ₅ and 21 ₆,the modulation decoder 20 finds the likelihood of the respectivecodewords and uses the likelihood values, thus found, to find theposterior probability information straightforwardly, as soft decisionvalues for the input and output bits on the modulation coder side.

Meanwhile, the modulation decoder 20 is fed from outside with log prioriprobability D25 ₁, D25 ₂, D25 ₃, D25 ₄. If the probability of therespective bits making up the binary signal input to the modulationcoder, not shown, being “0”, is equivalent to the same probability being“1”, there is no necessity of inputting the log priori probability D25₁, D25 ₂, D25 ₃, D25 ₄, it being only necessary to handle as if thevalues of these log priori probability D25 ₁, D25 ₂, D25 ₃, D25 ₄ areall equal to zero.

Although the above explanation is based on the assumption that themodulation decoder 20 decodes data obtained on modulation-coding a 2-bitinput to a 3-bit output, the modulation decoder is not limited as to thenumber of bits of the input or the output and may be similarlyconfigured in keeping with the number of bits of the input or the outputused.

Referring to FIG. 7, the magnetic recording and/or reproducingapparatus, employing this modulation decoder, is hereinafter explained.

A magnetic recording and/or reproducing apparatus 50, shown in FIG. 7,includes, as a recording system for recording data on a recording medium70, an error correction coder 51 for error correction coding input data,a modulation coder 52 for modulation coding input data, a precoder 53for filtering the input data for compensating for channelcharacteristics, a write current driver 54 for converting respectivebits of the input data into write current values, and a write head 55for recording data on a recording medium 70. The magnetic recordingand/or reproducing apparatus 50 also includes, as a reproducing systemfor reproducing data recorded on the recording medium 70, an equalizer57 for equalizing the input data, a gain adjustment circuit 58 foradjusting the gain of the input data, an analog/digital converter (A/Dconverter) 59 for converting analog data into digital data, a timingregenerating circuit 60 for regenerating clocks, a gain adjustmentcontrol circuit 61, a trellis SISO decoder 62, as a SISO type decoderfor trellis-decoding input data, a modulation SISO decoder 63, as a SISOtype decoder for modulation decoding input data and an error correctionsoft decoder 64 for error correction soft decoding input data.

The error correction coder 51 in the recording system error correctionencodes input data D51. The error correction coder 51 routes errorcorrection encoded data D52, generated on error correction coding, to adownstream side modulation coder 52.

The modulation coder 52, as the modulation encoding means,modulation-encodes the error correction encoded data D52, supplied fromthe error correction coder 51, to generate modulation coded data D53 asa string subjected to limitations. The modulation coder 52 routes thegenerated modulation coded data D53 to the downstream side precoder 53.

The precoder 53 filters the modulation coded data D53, supplied from themodulation coder 52, in such a manner as to compensate for channelcharacteristics from the data writing to the recording medium 70 to theoutputting thereof in the equalizer 57 in the reproducing system,thereby generating a precode signal D54 as a binary signal. For example,the precoder 53 performs filtering F represented by the followingequation (12):

F=1/(1⊕D)  (12)

if the channel of the precoder has 1−D characteristics. In the aboveequation, ⊕ denotes exclusive-OR. The precoder 53 sends the generatedprecede signal D54 to the downstream side write current driver 54.

The write current driver 54 converts respective bits of the precodesignal D54, supplied from the precoder 53, into the write current valueI_(S), so that 0 and 1 will be converted to −I_(S) and +I_(S)(0→−I_(S),1→+I_(S)), respectively, to generate a write current signal D55. Thewrite current driver 54 sends the so-generated write current signal D55to the downstream side write head 55.

The write head 55 routes a write magnetization signal D56, conforming tothe write current signal D55, supplied from the write current driver 54,to the recording medium 70 to record data thereon.

A readout head 56 in the reproducing system reads out the readoutmagnetization signal D57 from the recording medium 70 to generate areadout current signal D58 conforming to the readout magnetizationsignal D57. The readout head 56 sends the so-generated current signalD58 to the downstream side equalizer 57.

The equalizer 57 equalizes the current signal D58, supplied from thereadout head 56, so that the channel response from the data writing onthe recording medium 70 in the recording system up to the outputting atthe equalizer 57 will be of pre-set characteristics, such as the 1−D, togenerate an equalized signal D59. The equalizer 57 routes the generatedequalized signal D59 to the downstream side gain adjustment circuit 58.

Based on a gain adjustment control signal D63, supplied from the gainadjustment control circuit 61, the gain adjustment circuit 58 adjuststhe gain of the equalized signal D59 supplied from the equalizer 57, togenerate a gain adjustment signal D60. The gain adjustment circuit 58routes the generated gain adjustment signal D60 to the downstream sideA/D converter 59.

Based on the clock signal D62, supplied from the timing regeneratingcircuit 60, the A/D converter 59 samples and digitizes the gainadjustment signal D60, supplied from the gain adjustment circuit 58, togenerate a digital channel signal D61. The A/D converter 59 sends thegenerated digital channel signal D61 to the timing regenerating circuit60, gain adjustment control circuit 61 and to the trellis SISO decoder62.

The timing regenerating circuit 60 regenerates clocks from the digitalchannel signal D61 supplied from the A/D converter 59 to generate clocksignals D62. The timing regenerating circuit 60 sends the generatedclock signals D62 to the A/D converter 59.

Based on the digital channel signal D61, supplied from the A/D converter59, the gain adjustment control circuit 61 generates a gain adjustmentcontrol signal D63, which is a control signal used for maintaining theamplitude of the equalized signal D59 at an expected value. The gainadjustment control circuit 61 sends the generated gain adjustmentcontrol signal D63 to the gain adjustment circuit 58.

The trellis SISO decoder 62, as trellis decoding means, is fed from theA/D converter 59 with the digital channel signal D61, supplied from theA/D converter 59, to perform soft output decoding, based on theso-called BCJR (Bahl, Cocke, Jelinek and Raviv) algorithm or on the SOVA(Soft Output Viterbi Algorithm) algorithm, in accordance with thetrellis corresponding to the channel response from the pre-stage of theprecoder 53 in the recording system up to the outputting at theequalizer 57, for example, the channel response R_(ch) represented bythe following equation (13):

R _(ch)(1−D)/(1⊕D)  (13)

where ⊕ denotes exclusive-OR, to generate a trellis soft output signalD64. The trellis SISO decoder 62 routes the generated trellis softoutput signal D64 to the downstream side modulation SISO decoder 63.

The modulation SISO decoder 63, as modulation decoding means,constructed as the aforementioned modulation decoders 10, 20, is an SISOtype modulation decoder. The modulation SISO decoder 63, fed with thetrellis soft output signal D64 from the trellis SISO decoder 62,calculates a soft decision value for the error correction coded dataD52, input to the modulation coder 52 in the recording system, togenerate a modulated soft decision signal D65. This modulated softdecision signal D65 corresponds to the decoded log posterior probabilityratio D27 ₁, D27 ₂, represented by the above-mentioned log likelihoodratio. The modulation SISO decoder 63 sends the so-generated modulatedsoft decision signal D65 to a downstream side error correction softdecoder 64.

The error correction soft decoder 64, as error correction soft decodingmeans, soft-decodes the modulated soft decision signal D65 from themodulation SISO decoder 63 for error correction codes, which are basedon the aforementioned BCJR or SOVA algorithm, to output the soft-decodedsignals to outside as output data D66 of the soft or hard output.

In recording data on the recording medium 70, the magnetic recordingand/or reproducing apparatus 50 is able to record the precode signalD54, generated through the error correction coder 51, modulation encoder52 and the precoder 53, on the recording medium 70, through the writecurrent driver 54 and the write head 55.

In reproducing the data recorded on the recording medium 70, themagnetic recording and/or reproducing apparatus 50 soft-output-decodesthe digital channel signal D61, as a soft input generated by the readouthead 56, equalizer 57, gain adjustment circuit 58 and the A/D converter59, by the trellis SISO decoder 62, to generate the trellis soft outputsignal D64. The trellis soft output signal D64 corresponds to themodulation coded data D53 as an output of the modulation coder 52 of therecording system.

The magnetic recording and/or reproducing apparatus 50 thensoft-output-decodes the trellis soft output signal D64, as a soft input,supplied from the trellis SISO decoder 62, by the modulation SISOdecoder 63, to generate a modulated soft decision signal D65. Thismodulated soft decision signal D65 corresponds to the error correctioncoded data D52 fed to the modulation coder 52 of the recording system.

The magnetic recording and/or reproducing apparatus 50 soft-decodes themodulated soft decision signal D65, as a soft input, supplied from themodulation SISO decoder 63, by the error correction soft decoder 64, togenerate soft-output data. This soft-output data is directly output tooutside as output data D66, or is binary coded and turned into hardoutput data D66, which is output to outside.

The magnetic recording and/or reproducing apparatus 50, thus having theSISO type modulation decoder 62 in the reproducing system, is able toperform efficient decoding exploiting the soft information, so thatthere is no necessity to diminish the information and hence it becomespossible to lower the decoding error rate.

A magnetic recording and/or reproducing apparatus as a second embodimentis now explained. This magnetic recording and/or reproducing apparatusencodes data as correlation is afforded to the fore side data and aftside data in modulation coding and in modulation decoding, instead ofencoding/decoding the data on the block basis, while decoding the datain meeting with constraint conditions.

Referring to FIGS. 8 to 11, a modulation decoder of the SISO type, asmodulation encoding means applied to the recording system of themagnetic recording and/or reproducing apparatus, is first explained.

The magnetic recording and/or reproducing apparatus performs modulationencoding and modulation decoding, based on a common trellis. Althoughthe trellis structure is changed depending on the limitations imposed onthe modulation code, the modulation encoding and modulation decoding,satisfying the (d, k)=(0, 2) limitations, with the code rate R=2/3, ishere explained.

FIG. 8 shows a diagram showing the status transition for generatingsatisfying the (d, k)=(0, 2) limitations. In FIG. 8, labels affixedbetween the respective states indicate bits output in case of statustransition. For example, if the status transition that has occurred is“S0→S1→S2”, an output bit string is “00”. The bit string output in casestatus transition has occurred in accordance with the aforementionedstatus transition diagram necessarily satisfies the (d, k)=(0, 2)limitations.

Assume that the modulation encoding of outputting a 3 bit modulated codefor a 2-bit input, with the code rate R=2/3. For generating themodulation code satisfying the (d, k)=(0, 2) limitations, it isapparently sufficient if status transition occurs thrice in accordancewith the status transition diagram shown in FIG. 8, with the resultingoutput being a modulated code.

The trellis when the status transition has occurred thrice in accordancewith the status transition diagram shown in FIG. 8, that is, a diagramobtained on developing the status transition diagram along the time axisdirection, is as shown in FIG. 9. For example, in the trellis shown inFIG. 9, a branch lying at an uppermost position indicates that there isone path starting at the status S2 and again getting to the status S2after three status transitions, with a corresponding output being “100”.

In case of modulation encoding of outputting 3-bit modulated code for an2-bit input, 2²=4 branches are selected from each state, these branchesbeing then allocated to 2-bit inputs of “00, 01, 10, 11” to form atrellis in which an input is associated with an output. FIG. 10 shows atrellis formed on branch selection as described above. In FIG. 10, eachlabel affixed between different states indicate an input/output. Forexample, in the trellis shown in FIG. 10, a branch S0→S2 indicates that,if “11” is input for the state S0, status transition occurs to thestatus S2, as “100” is output.

The modulation encoder, applied to the magnetic recording and/orreproducing apparatus, shown as the second embodiment, repeats thestatus transition for encoding, in accordance with the trellis formed bythe above-described sequence of operations, to generate a modulated codestring having correlation between input data. The modulation encoder maybe provided with components shown for example in FIG. 11.

The modulation trellis encoder 80, shown in FIG. 11, includes a stateregister 81 for holding the state of the modulation trellis encoder 80,a next-state calculating circuit 82, for calculating the next transitionstate, and an output signal calculating circuit 83 for calculating anoutput signal D84.

The state register 81 is a 2-bit register holding 2 bits specifying thestate of the current modulation trellis encoder 80. The state register81 sends a status signal D82, specifying the 2 bits indicating thecurrent state, to the next-state calculating circuit 82 and to theoutput signal calculating circuit 83, as the state register 81 holds 2bits indicating the next state corresponding to the next state signalD83 supplied from the next-state calculating circuit 82.

When fed with the input signal D81 and with the status signal D82,supplied from the state register 81, the next-state calculating circuit82 calculates the next state in accordance with the followinginput/output correlating table 4:

TABLE 4 Typical Input/Output Correlating Table status signals inputsignals next-state signals 0 00 0 0 01 1 0 10 1 0 11 2 1 00 1 1 01 0 110 0 1 11 2 2 00 2 2 01 0 2 10 0 2 11 1 3 00 0 3 01 0 3 10 0 3 11 0

The next-state calculating circuit 82 sends the next state signal D83 tothe state register 81.

If fed with the input signal D81 and with the status signal D82,supplied from the state register 81, the output signal calculatingcircuit 83 calculates an output signal D84, in accordance with thefollowing input/output correlating table 5:

TABLE 5 Typical Input/Output Correlating Table status signals inputsignals output signals 0 00 111 0 01 110 0 10 010 0 11 100 1 00 110 1 01011 1 10 111 1 11 100 2 00 100 2 01 101 2 10 111 2 11 110 3 00 111 3 01111 3 10 111 3 11 111

Meanwhile, this output signal D84 satisfies the (d, k)=(0, 2)limitations.

When fed with the input signal D81, the modulation trellis encoder 80calculates the next state, using this input signal D81 and the statussignal D82, by the next-state calculating circuit 82, for storagesequentially in the state register 81. The modulation trellis encoder 80calculates an output signal D84, by the output signal calculatingcircuit 83, using the input signal D81 and the status signal D82, by theoutput signal calculating circuit 83, to output the so-calculated outputsignal D84.

Since there lacks the status S3 in the modulation trellis encoder 80, iftransition to the status S3 occurs before the resetting of themodulation trellis encoder 80, an output signal “111” is instantlyoutput as an output signal D84, based on the Table 5, to realize thefunction of resetting to the state S0.

A modulation decoder for modulation decoding the signal,modulation-encoded by the above-described modulation encoder, appliesthe decoding, which is based on the BCJR or SOVA algorithm, inaccordance with the trellis previously explained with reference to FIG.10. With this modulation decoder, the magnetic recording and/orreproducing apparatus is able to perform trellis decoding exploiting thesignal correlation in the modulation encoder.

In particular, if, in performing trellis decoding in the magneticrecording and/or reproducing apparatus, SISO decoding of the BCJR orSOVA algorithm is used in the modulation decoder, the soft informationcan be output to the error correction decoding circuit provideddownstream of the modulation decoder, thereby improving the decodingerror rate.

The magnetic recording and/or reproducing apparatus, employing this typeof the modulation encoder and the modulation decoder, is hereinafterexplained with reference to FIG. 12.

The magnetic recording and/or reproducing apparatus 100, shown in FIG.12, includes, as a recording system for recording data on a recordingmedium 70, an error correction encoder 101 for error correction encodinginput data, a modulation encoder 101, a modulation trellis encoder 102for modulation encoding input data, a precoder 103 for filtering inputdata for compensating its channel characteristics, a write currentdriver 104 for converting respective bits of the input data into writecurrent values, and a write head 105 for recording data on the recordingmedium 70. The magnetic recording and/or reproducing apparatus 200 alsoincludes, as a playback system for reproducing data recorded on therecording medium 70, a readout head 106 for reading out data recordingon the recording medium 70, an equalizer 107 for equalizing the inputdata, a gain adjustment circuit 108 for adjusting the gain of the inputdata, an analog/digital converter (A/D converter) 109 for convertinganalog data into digital data, a timing generating circuit 110 forgenerating clocks, a gain adjustment control circuit 111 for controllingthe gain adjustment circuit 108, a trellis SISO decoder 112, as adecoder for modulation decoding the input data, a modulation trellisSISO decoder 113, as an SISO decoder for modulation decoding the inputdata and an error correction soft decoder 114 for error correction softdecoding the input data.

Similarly to the error correction coder 51 in the magnetic recordingand/or reproducing apparatus 50, the error correction encoder 101 in therecording system applies error correction coding to the input data D101.The error correction encoder 101 sends the error correction encodeddata, generated on error correction encoding, to the downstream sidemodulation trellis encoder 102.

The modulation trellis encoder 102, as modulation encoding means, isconfigured as the aforementioned modulation encoder 80. Specifically, itis a modulation encoder for repeating status transitions in accordancewith the trellis, by way of encoding, for generating a modulated codestring exhibiting correlation between input data. The modulation trellisencoder 102 applies pre-set trellis modulation coding to the errorcorrection coded data D102, supplied from the error correction encoder101, to generate modulated encoded data D103 as a string subjected tolimitation. The modulation trellis encoder 102 sends the generatedmodulation encoded data D103 to the downstream side precoder 103.

Similarly to the precoder 53 of the aforementioned magnetic recordingand/or reproducing apparatus 50, the precoder 103 filters the modulationencoded data D 103, supplied from the modulation trellis encoder 102, insuch a manner as to compensate for channel characteristics from the datawriting to the recording medium 70 to the output in the equalizer 107 inthe reproducing system, thereby generating a precode signal D104 as abinary signal. The precoder 103 sends the so-generated precede signalD104 to the downstream side write current driver 104.

Similarly to the write current driver 54 in the aforementioned magneticrecording and/or reproducing apparatus 50, the write current driver 104converts respective bits of the precode signal D104, supplied from theprecoder 103, into the write current value I_(S), to generate a writecurrent signal D105. The write current driver 104 sends the generatedwrite current signal D105 to a downstream side write head 105.

Similarly to the write head 55 in the aforementioned magnetic recordingand/or reproducing apparatus 50, the write head 105 applies a writemagnetization signal D106, corresponding to the write current signalsupplied from the write current driver 104, to the recording medium 70,to record data thereon.

Similarly to the write head 56 in the aforementioned magnetic recordingand/or reproducing apparatus 50, the readout head 106 in the reproducingsystem reads out the readout magnetization signal D107 from therecording medium 70 to generate a readout current signal D108 conformingto the readout magnetization signal D107. The readout head 56 sends theso-generated current signal D108 to the downstream side equalizer 107.

Similarly to the equalizer 57 in the aforementioned magnetic recordingand/or reproducing apparatus 50, the equalizer 107 equalizes the currentsignal D108, supplied from the readout head 106, so that the channelresponse from the data writing on the recording medium 70 in therecording system up to the outputting at the equalizer 107 will bepre-set characteristics, to generate an equalized signal D109. Theequalizer 107 routes the generated equalized signal D109 to thedownstream side gain adjustment circuit 108.

Similarly to the gain adjustment circuit 58 in the aforementionedmagnetic recording and/or reproducing apparatus 50, the gain adjustmentcircuit 108 adjusts the gain of the equalized signal D59, supplied fromthe equalizer 57, based on a gain adjustment control signal D113,supplied from the gain adjustment control circuit 111, to generate again adjustment signal D110. The gain adjustment circuit 108 routes thegenerated gain adjustment signal D110 to the downstream side A/Dconverter 109.

Similarly to the A/D converter 59 of the aforementioned magneticrecording and/or reproducing apparatus 50, the A/D converter 109 samplesand digitizes the gain adjustment signal D110, supplied from the gainadjustment circuit 108, based on the clock signal D112, supplied fromthe timing regenerating circuit 110, to generate a digital channelsignal D111. The A/D converter 109 sends the generated digital channelsignal D111 to the timing reproducing circuit 110, gain adjustmentcontrol circuit 111 and to the trellis SISO decoder 112.

Similarly to the timing regenerating circuit 60 in the aforementionedmagnetic recording and/or reproducing apparatus 50, the timingregenerating circuit 110 regenerates clocks from the digital channelsignal D111 supplied from the A/D converter 109 to generate clocksignals D112. The timing regenerating circuit 110 sends the generatedclock signals D112 to the A/D converter 109.

Similarly to the gain adjustment control circuit 61 of the magneticrecording and/or reproducing apparatus 50, the gain adjustment controlcircuit 111 generates a gain adjustment control signal D113, which is acontrol signal used for maintaining the amplitude of the equalizedsignal D109 at an expected value, based on the digital channel signalD111, supplied from the A/D converter 109. The gain adjustment controlcircuit 111 sends the generated gain adjustment control signal D113 tothe gain adjustment circuit 108.

Similarly to the trellis SISO decoder 62 of the aforementioned magneticrecording and/or reproducing apparatus 50, the trellis SISO decoder 112,as trellis decoding means, is fed with the digital channel signal D111from the A/D converter 109, and performs soft output decoding, based onthe aforementioned BCJR or SOVA algorithm, in accordance with thetrellis corresponding to the channel response from the forward stage ofthe precoder 103 in the recording system to the output of the equalizer107 of the reproducing system, to generate the trellis soft outputsignal D114. The trellis SISO decoder 112 sends the so-generated trellissoft output signal D114 to the downstream side modulation trellis SISOdecoder 113.

The modulation trellis SISO decoder 113, as modulation decoding means,used for decoding signals encoded by the modulation trellis encoder 102in the recording system, is an SISO type modulation decoder. Themodulation trellis SISO decoder 113, fed with the trellis soft outputsignal D114 from the trellis SISO decoder 112, finds a soft decisionvalue for the error correction coded data D102, input to the modulationtrellis coder 102 in the recording system, to generate a modulated softdecision signal D115. The modulation trellis SISO decoder 113 sends theso-generated modulated soft decision signal D115 to a downstream sideerror correction soft decoder 114.

Similarly to the error correction soft decoder 54 in the magneticrecording and/or reproducing apparatus 50, the error correction softdecoder 114, as error correction soft decoding means, soft-decodes themodulated soft decision signal D115 from the modulation trellis SISOdecoder 113 for error correction codes, based on the aforementioned BCJRor SOVA algorithm, to output the soft-decoded signals to outside as thesoft or hard output data D 116.

In recording data on the recording medium 70, the magnetic recordingand/or reproducing apparatus 100 is able to apply trellis modulationcoding to the error correction coded data D102, generated by the errorcorrection encoder 101, by the modulation trellis encoder 102, togenerate modulated encoded data D103. The magnetic recording and/orreproducing apparatus 100 is also able to record the precode signalD104, generated through the precoder 103, on the recording medium 70,through the write current driver 104 and the write head 105.

In reproducing the data recorded on the recording medium 70, themagnetic recording and/or reproducing apparatus 100 soft-output-decodesthe digital channel signal D111, as a soft input generated by thereadout head 106, equalizer 107, gain adjustment circuit 108 and the A/Dconverter 109, by the trellis SISO decoder 112, to generate the trellissoft output signal D114. The trellis soft output signal D114 correspondsto the modulation coded data D103 which is an output of the modulationcoder 102 of the recording system.

The magnetic recording and/or reproducing apparatus 100 thensoft-output-decodes the trellis soft output signal D114, as a softinput, supplied from the trellis SISO decoder 112, by the modulationSISO decoder 113, to generate a modulated soft decision signal D115.This modulated soft decision signal D115 corresponds to the errorcorrection coded data D102 fed to the modulation coder 102 of therecording system.

The magnetic recording and/or reproducing apparatus 100 soft-decodes themodulated soft decision signal D115, as a soft input, supplied from themodulation SISO decoder 113, by the error correction soft decoder 114,to generate soft-output data. This soft-output data is directly outputto outside as output data D66, or is binary coded and turned into hardoutput data D116, which is output to outside.

The magnetic recording and/or reproducing apparatus 100, thus having theSISO type modulation trellis SISO decoder 112 in the reproducing system,is able to perform efficient decoding exploiting the soft information.Moreover, the magnetic recording and/or reproducing apparatus 100includes the modulation trellis encoder 102 performing trellismodulation coding in the recording system, so that encoding can be madeas correlation is afforded to the fore and aft side data. In addition,trellis decoding can be made by the SISO type modulation trellis SISOdecoder 112 in meeting with the constraint condition, thus furtherlowering the decoding error rate.

The above-described magnetic recording and/or reproducing apparatus 50,100 are able to perform efficient decoding by exploiting the softinformation, thereby lowering the decoding error rate. In particular,with the magnetic recording and/or reproducing apparatus 100, encodingcan be made as correlation is afforded to the fore and aft side data,without doing block-based encoding or decoding, while trellis decodingcan be made in meeting with the constraint conditions, thus furtherlowering the decoding error rate. That is, the magnetic recording and/orreproducing apparatus 50, 100 is able to realize high precisiondecoding, thus assuring high operational reliability fort the user.

The present invention is not limited to the above-described embodiment.For example, the present invention may be applied to a recording medium70 other than the recording medium of the magnetic recording system,that is to a recording medium by the optical recording system, such as aso-called CD (Compact Disc) or to the DVD (Digital Versatile Disc) or toa recording medium of the photomagnetic recording system, such as aso-called magneto-optical disc (MO) disc.

In the above-described embodiment, it is assumed that the magneticrecording and/or reproducing apparatus 100 performs trellis modulationencoding on the encoder side and trellis modulation decoding on thedecoder side. However, the present invention is applicable to such acase wherein the trellis modulation decoding is performed on the decoderside to output a soft decision value even in case the trellis modulationencoding is not performed on the encoding side.

Moreover, in the above-described embodiment, it is assumed that themagnetic recording and/or reproducing apparatus 50 or 100 is a unitaryapparatus provided with the recording and reproducing systems.Alternatively, a unitary recording apparatus may be configured as arecording system for recording data on a recording medium, while aunitary reproducing apparatus may also be configured as a reproducingsystem for reproducing the data recorded on the recording apparatus.

In the foregoing, the present invention has been disclosed only by wayof illustration and should not be interpreted in a limiting fashion. Thescope of the present invention is to be interpreted in light of thedescription of the following claims.

What is claimed is:
 1. A data reproducing apparatus for reproducing datarecorded on a recording medium comprising: trellis soft input softoutput (SISO) modulation decoding means for modulation decoding datathat is modulation-encoded in a predetermined fashion by modulationencoding means to generate a trellis soft output signal; and modulationSISO decoding means that is fed with the trellis soft output signal forcalculating a soft decision value for error correction coded data togenerate a modulated soft decision signal; said modulation SISO decodingmeans outputting a soft output signal in order to lower a decoding errorrate.
 2. The data reproducing apparatus according to claim 1 whereinsaid modulation encoding means performs encoding under a constraintcondition; and wherein said modulation SISO decoding means performs softoutput decoding in meeting with said constraint condition.
 3. The datareproducing apparatus according to claim 2 wherein said modulation SISOdecoding means includes: likelihood calculating means for calculatingthe likelihood value corresponding to each output codeword output bysaid modulation encoding means; said modulation SISO decoding meansfinding the posterior probability information as soft decision value foran input bit fed to said modulation encoding means and an output bitissued from said modulation encoding means, using the likelihood valuecalculated by said likelihood calculating means.
 4. The data reproducingapparatus according to claim 2 wherein said modulation encoding meansperforms encoding in accordance with the trellis corresponding to saidconstraint condition; said modulation SISO decoding means performingsoft output decoding based on the trellis corresponding to saidconstraint condition.
 5. The data reproducing apparatus according toclaim 4 wherein said trellis SISO modulation decoding means performstrellis decoding based on the BCJR (Bahl, Cocke, Jelinek and Raviv)algorithm or the SOVA (Soft Output Viterbi Algorithm) algorithm.
 6. Thedata reproducing apparatus according to claim 2 further comprising:trellis SISO modulation decoding means for performing soft outputdecoding on a soft input signal based on the trellis corresponding to achannel response; and error correcting soft decoding means forperforming soft decoding of error correction codes on a soft inputsignal; said modulation SISO decoding means being fed with the softtrellis output signal, as a soft output, from said trellis SISOmodulation decoding means, to find a soft decision value for errorcorrection data input to said modulation encoding means to route amodulation soft decision signal as a soft output to said errorcorrection soft decoding means.
 7. The data reproducing apparatusaccording to claim 1 wherein the recording medium is such that data isrecorded in accordance with a magnetic, optical or magneto-opticalrecording system.
 8. A data reproducing method for reproducing datarecorded on a recording medium comprising the steps of: reproducingtrellis soft input soft output (SISO) modulation-encoded data from saidrecording medium, being encoded in a predetermined fashion in amodulation encoding step to generate a trellis soft output signal; andmodulation SISO decoding the reproduced modulation-encoded data that isfed with the trellis soft output signal for calculating a soft decisionvalue for error correction coded data to generate a modulated softdecision signal, said modulation SISO decoding step outputting a softoutput signal in order to lower a decoding error rate.
 9. The datareproducing method according to claim 8 wherein said modulation encodingstep performs encoding under a constraint condition; and wherein saidmodulation SISO decoding step performs soft output decoding in meetingwith said constraint condition.
 10. The data reproducing methodaccording to claim 9 wherein said modulation SISO decoding stepincludes: a likelihood calculating step for calculating the likelihoodvalue corresponding to each output codeword output in said modulationencoding step; said modulation SISO decoding step finding the posteriorprobability information as a soft decision value for an input bit fed insaid modulation encoding step and an output bit issued from saidmodulation encoding step, using the likelihood value as found by saidlikelihood calculating step.
 11. The data reproducing method accordingto claim 9 wherein said modulation encoding step performs encoding inaccordance with the trellis corresponding to said constraint condition;said modulation SISO decoding step performing soft output decoding basedon the trellis corresponding to said constraint condition.
 12. The datareproducing method according to claim 11 wherein said trellis SISOmodulation decoding step performs trellis decoding based on the BCJR(Bahl, Cocke, Jelinek and Raviv) algorithm or the SOVA (Soft OutputViterbi Algorithm) algorithm.
 13. The data reproducing method accordingto claim 9 further comprising: a trellis SISO modulation decoding stepfor performing soft output decoding on an input signal as a soft inputsignal based on the trellis corresponding to a channel response; and anerror correcting soft decoding step of performing soft decoding of errorcorrection codes in said soft input signal; said modulation SISOdecoding step being fed with the soft trellis output signal, as a softoutput, generated in said trellis SISO modulation decoding step, to finda soft decision value for error correction data input in said modulationencoding step to generate a modulation soft decision signal as a softoutput; said error correction soft decoding step performing softdecoding of error correction coded data of said modulation soft decisionsignal.
 14. The data reproducing method according to claim 8 wherein therecording medium is such that data is recorded in accordance with amagnetic, optical or magneto-optical recording system.
 15. A datarecording and reproducing apparatus for recording and reproducing dataon a recording medium, comprising: modulation encoding means forperforming predetermined modulation encoding on said data to be recordedon said recording medium; and modulation SISO decoding means formodulation-decoding the modulation-encoded data reproduced from saidrecording medium that is fed with a trellis soft output signal forcalculating a soft decision value for error correction coded data togenerate a modulated soft decision signal; said modulation SISO decodingmeans outputting a soft output signal in order to lower a decoding errorrate.
 16. The data recording and reproducing apparatus according toclaim 15 wherein said modulation encoding means performs encoding inaccordance with a constraint condition; and wherein said modulation SISOdecoding means performs soft output decoding in meeting with saidconstraint condition.
 17. The data recording and reproducing apparatusaccording to claim 16 wherein said modulation SISO decoding meansincludes: likelihood calculating means for calculating the likelihoodvalue corresponding to each output codeword issued from said modulationencoding means; wherein the posterior probability information as softdecision values for an input bit fed to said modulation encoding meansand an output bit issued from said modulation encoding means.
 18. Thedata recording and reproducing apparatus according to claim 16 whereinsaid modulation encoding means performs encoding in accordance with thetrellis corresponding to said constraint condition; said modulation SISOdecoding means performing soft output decoding based on the trelliscorresponding to said constraint condition.
 19. The data recording andreproducing apparatus according to claim 18 wherein a trellis SISOmodulation decoding means performs trellis decoding based on the BCJR(Bahl, Cocke, Jelinek and Raviv) algorithm or the SOVA (Soft OutputViterbi Algorithm) algorithm.
 20. The data recording and reproducingapparatus according to claim 16, further comprising: trellis SISOmodulation decoding means for performing soft output decoding on a softinput signal based on the trellis corresponding to a channel response;and error correcting soft decoding means for performing soft decoding oferror correction codes of a soft input signal; said modulation SISOdecoding means being fed with the soft trellis output signal, as a softoutput, from said trellis SISO modulation decoding means, to find a softdecision value for error correction data input to said modulationencoding means to route a modulation soft decision signal as a softoutput to said error correction soft decoding means.
 21. The datarecording and reproducing apparatus according to claim 15 wherein therecording medium is such that data is recorded in accordance with amagnetic, optical or magneto-optical recording system.
 22. A datarecording and reproducing method for recording and reproducing data fora recording medium, comprising the steps of: performing predeterminedmodulation encoding on said data; recording the modulation-encoded dataon said recording medium; reproducing trellis soft input soft output(SISO) modulation-encoded data from said recording medium to generate atrellis soft output signal; and modulation SISO decoding said reproducedmodulation-encoded data that is fed with the trellis soft output signalfor calculating a soft decision value for error correction coded data togenerate a modulated soft decision signal, said modulation SISO decodingstep being outputting a soft output signal in order to lower a decodingerror rate.
 23. The data recording and reproducing method according toclaim 22 wherein said modulation encoding step performing encoding inaccordance with a constraint condition; and wherein said modulation SISOdecoding step performs soft output decoding in meeting with saidconstraint condition.
 24. The data recording and reproducing methodaccording to claim 23 wherein said modulation SISO decoding stepincludes: a likelihood calculating step of calculating the likelihoodvalue corresponding to each output codeword output by said modulationencoding step; wherein the posterior probability information as a softdecision value for an input bit fed in said modulation encoding step andan output bit issued from said modulation encoding step, using thelikelihood value calculated in said likelihood calculating step.
 25. Thedata recording and reproducing method according to claim 23 wherein saidmodulation encoding step performs encoding in accordance with thetrellis corresponding to said constraint condition; said modulation SISOdecoding step performing soft output decoding based on the trelliscorresponding to said constraint condition.
 26. The data recording andreproducing method according to claim 25 wherein said trellis SISOmodulation decoding step performs trellis decoding based on the BCJR(Bahl, Cocke, Jelinek and Raviv) algorithm or the SOVA (Soft OutputViterbi Algorithm) algorithm.
 27. The data recording and reproducingmethod according to claim 23, further comprising: a trellis SISOmodulation decoding step for performing soft output decoding on a softinput signal based on the trellis corresponding to channel response; andan error correcting soft decoding step of performing soft decoding oferror correction codes of a soft input signal; said modulation SISOdecoding step being fed with the soft trellis output signal, as a softoutput, from said trellis SISO modulation decoding step, to find a softdecision value for error correction data input to said modulationencoding step to generate a modulation soft decision signal as a softoutput; said error correction soft decoding step soft-decoding errorcorrection codes of said modulation soft decision signal.
 28. The datareproducing method according to claim 22 wherein the recording medium issuch that data is recorded in accordance with a magnetic, optical ormagneto-optical recording system.